The Plant Conservation Alliance is devoted to saving native plants and plant habitats in the US. It's a consortium of 10 federal agencies allied with around 260 non-federal experts (from scientists to "nature lovers," according to the FAQ). The PCA awards grants for on-the-ground projects to conserve native plants, and also convenes participants via via meetings and email lists -- which anyone can join. It looks like there may be a wealth of information here on preserving native biodiversity, as well as a great network of people to tap into to both learn more and contribute.